The invention relates to an optoelectronic measuring device for monitoring combustion processes in the combustion chamber of an internal combustion engine during operation, with optical sensors assigned to the combustion chamber, which are connected to an evaluation unit, each sensor being provided with a lens assembly at its point of entrance into the combustion chamber, which lens assembly is in optical contact with at least one optical fiber and includes a plano-convex lens as focusing lens, and an end of at least one optical fiber being positioned in a focal plane of the focusing lens.